COMMISSION 27 OF THE I. A. U.
             INFORMATION BULLETIN ON VARIABLE STARS
                         Number 3627

                                                  Konkoly Observatory
                                                  Budapest
                                                  19 June 1991

                                                  HU ISSN 0374 - 0676


                       "QUASIALGOL" BO Cep


The light curve of the rapid irregular variable star BO Cep with Algol-like
sharp non-periodic minima was investigated by Hoffmeister (1949), Zajtseva
(1971), Wenzel and Bruckner (1978), Kovalchuk and Pugach (1980), Kardopolov
and Shutiomova (1980). A satisfactory period could not be found. The spectral
type was determined as F2 (Herbig, 1960). A weak emission in H alpha line
(EW_lambda H_alpha = 4.6 A, V_r H_alpha = -45 km/s) was discovered by
Zajtseva and Kolotilov (1973).

Our own observations were made in 1987-1990 on mt. Maidanak using the 0.5 m
reflector with UBVR-pulse counting photometer and, besides, on October 20, 1988
with the Byurakan 2.6-m reflector with the UAGS spectrograph with 100
A/mm dispersion and equipped with an image tube.

The photometric data are given in Table I. They were investigated by a program
of Fourier-analysis, dispersion curve analysis and Kurochkin - Jurkevich
method. 12 Algol-like weakenings were excluded from the calculations. The
light curve folded with the photometric elements 2446364.567+10.658d E for 4
years of observations is plotted in Figure 1. Figure 2 shows that both r.m.s.
and the average level of the light curve change from year to year. Moreover,
minima typical of eclipsing binaries with the amplitude not less than 0.05m V
were observed in 1987 and 1990. Algol-like light weakenings with an amplitude
of <0.5m V and duration <1d occur on an average once per 40 days and are
observed near phase 0.0 +- 0.15. Some Algol-like non-periodic minima are
observed very close to phase 0.0. So, minima 2443689.34 and 2443710.31
(Kardopolov, Shutiomova, 1980) indicate 10.6558d period. Algollike weakenings
are comparatively seldom near phase 0.5 +-0.3 and have lower amplitudes.

The spectrum of BO Cep at 4600-6100 A on the scale of intensities is
given in Figure 3. The spectrum is an average of 3 spectrograms. In
accordance with H beta, Fe I, Ca I line intensities the spectral type of BO Cep
is F2. The H beta line does not show any emission. There is some probability
of finding a weak emission in Mg I doublet 5172, 5179 A. The Na D line
is very wide.

                      Table I. Photometric data

J.D.2400000+   n    V_max  V_min   <V>   delta V <U-B> <B-V> <V-R>
48888- 47178  67    11.53  11.80  11.598  0.026  -0.04  0.54   0.54
47307- 47549  137   11.47  11.97  12.582  0.024  -0.03  0.54   0.59
47690- 47887  109   11.51  11.97  11.615  0.027  -0.03  0.55   0.54
48049- 48234  110   11.58  11.82  11.618  0.024  -0.05  0.55   0.54


                                [FIGURE 1]

           Figure 1. BO Cep summary light curve within 4 years

Wenzel (1977) and Pugach (1981) could ground with sufficient certainty that
non-periodic minima occur due to irregular weakenings of the main star by dust
fractions. The excess E_U-B=-0.05m+/- 0.1m (Wenzel, Bruckner, 1978) U-B gives
some indication that dust is present in BO Cep system.


                                [FIGURE 2]

             Figure 2. Light curve of BO Cep for each year

                                [FIGURE 3]

               Figure 3. Spectrum of BO Cep at 4600-6100 A


We suggest that BO Cep is a binary with the orbital plane inclination i ~ 5d
and the period of rotation P=10.658d. The invisible component is surrounded
by a nonstable dust shell with radius changing within its Roche lobe. The
shell increasing leads to a partial eclipse. The reflection (phase) effect is
essential. Sharp non-periodic minima occur when the dust fragments leave the
shell through the inner Lagrangian point, rush to the main star and cause the
darkening near its photosphere. A weak variable H alpha emission can be
influenced by the accretion.

RZ Psc shows a similar light curve with 13.78d period. We offer to call such
systems "quasialgols".


K.N. GRANKIN, M.A. IBRAGIMOV, S.Yu. MELNIKOV, V.S. SHEVCHENKO, S.D. YAKUBOV
            Tashkent Astronomical Institute, USSR

G.V. ABRAMIAN, N.D. MELIKIAN          I. JANKOVICS
Byurakan Observatory,                 Konkoly Observatory,
Armenia, USSR                         Budapest
                                      Gothard Observatory,
                                      Szombathely,
                                      Hungary

References:

Herbig, G.H.: 1960, Lick Contr. ser II, No. 102.
Hoffmeister, C.: 1949, Astron. Nachr., 278, 24. [BIBCODE 1949AN....278...24H ]
Kardopolov, V.I., Shutiomova, N.A.: 1980, Perem. Zvezdy, 21, 3. [BIBCODE 1980PZ.....21..305K ]
Kovalchuk, G.U., Pugach, A.F.: 1980, Mitt. Veranderl. Sterne, 8.
Pugach, A.F.: 1981, Astrofisika, 17, 87. [BIBCODE 1981Afz....17...87P ]
Wenzel, W.: 1977, in "Flare Stars", ed. L.V. Mirzoyan, Yerevan, p.105.
Wenzel, W., Bruckner, V.: 1978, Mitt. Veranderl. Sterne, 8, 35. [BIBCODE 1978MitVS...8...35W ]
Zajtseva, G.V.: 1971, Astron. Tsirk., 628, 3. [BIBCODE 1971ATsir.628....3Z ]
Zajtseva, G.V., Kolotilov, E.A.: 1973, Astrofisika, 9, 185. [BIBCODE 1973Afz.....9..185Z ]